The present invention relates to a fuel cell cogeneration system generating electric power and heat, particularly to a cogeneration system using a solid polymer electrolyte fuel cell.
The solid polymer electrolyte fuel cell generates electric power by reacting fuel gas, such as hydrogen, with oxidant gas, such as oxygen. This reaction also generates heat simultaneously with electric power. The solid polymer electrolyte fuel cell cogeneration system supplies the electric power and heat thus generated to an external load.
FIG. 4 shows a conventional solid polymer electrolyte fuel cell cogeneration system.
A fuel gas generating unit 9, e.g. reformer heats a raw material, such as natural gas, supplied from the outside in a steam atmosphere to generate hydrogen-rich fuel gas. A fuel cell 1 is supplied with fuel gas and oxidant gas such as air which are humidified by respective humidifiers 17 and 18.
Direct current (DC) generated by the fuel cell 1 is converted to alternating current (AC) by an inverter 2 and subsequently supplied to a power load, grid-connected with commercial electric power supply. In other words, when an output from the cogeneration system exceeds the power load, excess power is xe2x80x9csoldxe2x80x9d to a utility.
The heat generated by the fuel cell 1, on the other hand, is supplied to a hot-water supply load such as hot-water supply or heating, for example.
A cooling pump 6 circulates cooling water to the fuel cell 1 in order to recover the heat generated by the fuel cell 1.
A storage tank 13 stores city water. A three way valve 7 is usually connected between points A and B as shown in the figure when the system is operated, and the, cooling water is cooled by a heat exchanger 3 located at a bottom of the storage tank 13 after passing through the fuel cell 1. As a result, water in the storage tank 13 is heated. Hot water thus obtained is utilized. by the hot-water supply load such as heating. The cooling water which has a low temperature due to heat loss, on the other hand, is recirculated to the fuel cell 1. When water in the storage tank 13 is heated sufficiently, the three way valve 7 is connected at points A and C and the heat of the cooling water passing through the fuel cell 1 is discharged outside the system by a radiator 11.
The conventional fuel cell cogeneration system as shown above primarily heats water at the bottom of the storage tank 13, which generates convection of water in the storage tank 13. This corrects a temperature difference of water in the storage tank 13 but inversely increases time for supplying hot water after the system starts to operate. In order to cope with a large-size hot water supply load, it is necessary to prepare another hot water supplying apparatus for supplemental heating.
The object of the present invention is to provide a solid polymer electrolyte fuel cell cogeneration system which solves the above-mentioned drawbacks of the prior art system and can not only stably supply hot water at high temperature shortly after the system starts to operate but also readily cope with changes in power load and a large hot-water supply load.
The solid polymer electrolyte fuel cell cogeneration system in accordance with the present invention comprises a solid polymer electrolyte fuel cell for generating electric power and heat by reacting fuel gas with oxidant gas; a fuel gas generating unit for generating fuel gas; an inverter for supplying electric power to an external power load by converting DC output from the fuel cell to AC; a cooling water circulating path for circulating cooling water for recovering heat generated by the fuel cell or fuel gas generating unit; a storage tank for reserving hot water to be supplied to an external hot-water supply load; a heat exchanger for transferring heat recovered by the cooling water to water in the storage tank; a heating path connected to the storage tank; and a pump for passing water in the storage tank through the heat exchanger, the heating path having the heat exchanger, wherein a water inlet of the heating path and a water filling port for supplying water to the storage tank from the outside of the system are formed both at a lower part of the storage tank, and wherein a water outlet of the heating path and a hot-water supply port for supplying hot water in the storage tank to the external hot-water supply load are provided both at an upper part of the storage tank.
In a preferred mode of the present invention, the solid polymer electrolyte fuel cell cogeneration system further comprises a heater provided in the heating path for passing water in the storage tank through the heat exchanger and a detector for detecting a magnitude of the external power load.
In another preferred mode of the present invention, the solid polymer electrolyte fuel cell cogeneration system further comprises controlling means. for supplying excess electric power to the heater, based on such a detection signal that a magnitude of the external power load detected by the detector is smaller than output electric power of the fuel cell.
In still another preferred mode of the present invention, the solid polymer electrolyte fuel cell cogeneration system further comprises a thermodetector for detecting a temperature of water in the storage tank. It is also desirable to provide controlling means for supplying output electric power of the fuel cell to the heater when a temperature of water detected by the thermodetector decreases lower than a predetermined value.
In still another preferred mode of the present invention, the solid polymer electrolyte fuel cell cogeneration system further comprises another thermodetector for detecting a temperature of water passing through the heat exchanger and means for controlling the pump in such a way that a temperature of water detected by the thermodetector is kept constant, both being provided further down the heat exchanger in the heating path.
While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings.